Process for preparing an aqueous solution of sulfanilic acid modified melamine-formaldehyde resin and a cement composition

ABSTRACT

The present invention relates to a process for preparing an aqueous solution of sulfonated melamine-formaldehyde resin, and a cement composition in which the solution and a setting retarder are added to a concrete, a mortar, a cement paste or the like. And the process comprises the following step (A), step (B) and step (C): 
     Step (A): a step of adjusting an aqueous solution containing melamine (a), formaldehyde (b), sulfanilic acid (c) and an alkali substance (d) to (a):(b):(c)=1:2.5-3.5:0.5-1.5 in molar ratio and its pH to 8.0-13.5, and thereafter heating the aqueous solution at 50-90° C. to conduct the reaction until free sulfanilic acid decreases to 40-90 mol % of the amount of sulfanilic acid charged; 
     Step (B): a step of adding an inorganic acid to the reaction liquid obtained in the step (A) to adjust its pH to 6.0-8.0, and thereafter heating the reaction liquid at 50-90° C. to conduct the reaction until free sulfanilic acid decreases to 20-60 mol % of the amount of sulfanilic acid charged; 
     Step (C): a step of adjusting a pH of the reaction liquid obtained in step (B) to 7.0-13.5.

This is a Division of application Ser. No. 09/420,235 filed Oct. 19,1999, now U.S. Pat. No. 6,214,965. The entire disclosure of the priorapplication is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for preparing an aqueoussolution of sulfonated melamine-formaldehyde resin, and a cementcomposition in which the solution and a setting retarder are added to aconcrete, a mortar, a cement paste or the like.

2. Description of the Related Art

An aqueous solution of sulfonated melamine-formaldehyde resin hasconventionally been used as a dispersant for cement for the purpose ofincreasing fluidity of a cement composition such as a concrete or amortar, or decreasing a unit amount of water thereby increasing strengthand durability.

Some proposals relating to the improvement in a process for preparingsuch a water reducing agent have been disclosed.

JP-A-55-7590 discloses a melamine-urea formaldehyde condensate modifiedwith an aromatic aminosulfonic acid. Further, its molar ratio is definedsuch that the aromatic aminosulfonic acid to the total of melamine andurea is (0.2-1.0):1.0, and the molar ratio of melamine to urea isdefined 0.75:0.25 to 0.30:0.70.

JP-B-1-40850 discloses a process for preparing an aqueous solution ofmelamine/aldehyde resin, which comprises:

step (a) of reacting 1 mole of melamine, 3.5-6 moles of formaldehyde and0.5-1 moles of a compound 1 (wherein the compound 1 is at least onemember selected from the group consisting of a sulfite of an alkalimetal, a sulfite of an alkaline earth metal, a sulfate of an alkalimetal, a sulfate of an alkaline earth metal, aminosulfonic acid, aminoacid, aminodicarboxylic acid, hydroxycarboxylic acid, hydroxycarboxylicacid lactone, sulfanilic acid and sulfamic acid) in an alkaline mediumhaving a pH of 9.0-13.0 in which water is present, at a temperature of75-90° C.; step (b) of reacting the mixture obtained in the step (a)with 0.1-3 moles, per mole of melamine used in the step (a), of acompound 2 (wherein the compound 2 is at least one member selected fromthe group consisting of amino acid, aminocarboxylic acid,aminodicarboxylic acid, carboxylic acid, hydroxycarboxylic acid,hydroxycarboxylic acid lactone, sulfamic acid, sulfanilic acid,aminosulfonic acid, polyhydroxycarboxylic acid and polyhydroxycarboxylicacid lactone at a pH of 5.5-6.5 and a temperature of 75-90° C.; step (c)of adding a basic compound 3 (wherein the basic compound 3 is at leastone member selected from the group consisting of an amine, a polyamine,an oxide of an alkali metal, a hydroxide of an alkaline metal, ammoniumhydroxide, an oxide of an alkaline earth metal, monoethanol amine,diethanol amine, triethanol amine, a basic salt of a transition metaland a basic salt of zinc or aluminum) to the resin solution obtained inthe step (b) to adjust a pH of the solution to 8.0-13.0, and thencooling the solution obtained in the step (c).

DE 441197 discloses a process for preparing an aqueous solution ofsulfonated melamine-formaldehyde resin by adjusting the ratio ofmelamine, sulfanilic acid and formaldehyde to 1:1.1-1.5:3.3-3.6,adjusting a pH of a mixed solution to 5.0-7.0, heating the solution at50-90° C., and adjusting a viscosity to 10-60 cSt (80° C.).

Conventional water reducing agents comprising a sulfonatedmelamine-formaldehyde resin as a main component have had the defect inthat time for retaining fluidity of a cement composition is short, thatis, the fluidity lowers with the passage of time. For this reason, thewater reducing agent is mainly used in a concrete secondary productfactory, it is used as a fluidizing agent in a ready-mixed concrete, andit is not well used in a ready-mixed concrete production plant. Inparticular, this tendency is strong in Japan.

In JP-A-55-7590, JP-B-1-40850 and DE 441197, it is difficult to preventdecrease of the fluidity, and it is therefore difficult to use in theready mixed concrete production plant.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above conventionalproblems.

One object of the present invention is to provide a process forpreparing an aqueous solution of a water reducing agent using asulfanilic acid modified melamine-formaldehyde resin which has highperformance as a water reducing agent and prevents fluidity of aconcrete from lowering with the passage of time, without time-extendingfor complete setting and entraining air.

Another object of the present invention is to provide a cementcomposition in which an aqueous solution of sulfonatedmelamine-formaldehyde resin (for example, a sulfanilic acid modifiedmelamine-formaldehyde resin, or a melamine-formaldehyde resin modifiedwith other sulfonating agents) and a setting retarder are added to aconcrete, a mortar, a cement paste or the like.

A first aspect of the present invention is a process for preparing anaqueous solution of melamine-formaldehyde resin modified with sulfanilicacid, which comprises the following step (A), step (B) and step (C):

Step (A): a step of adjusting an aqueous solution containing melamine(a), formaldehyde (b), sulfanilic acid (c) and an alkali substance (d)to (a):(b):(c)=1:2.5-3.5:0.5-1.5 in molar ratio and its pH to 8.0-13.5,and thereafter heating the aqueous solution at 50-90° C. to conduct thereaction until free sulfanilic acid decreases to 40-90 mol % of theamount of sulfanilic acid charged;

Step (B): a step of adding an inorganic acid to the reaction liquidobtained in the step (A) to adjust its pH to 6.0-8.0, and thereafterheating the reaction liquid at 50-90° C. to conduct the reaction untilfree sulfanilic acid decreases to 20-60 mol % of the amount ofsulfanilic acid charged;

Step (C): a step of adjusting a pH of the reaction liquid obtained instep (B) to 7.0-13.5.

A second aspect of the present invention is a cement compositioncomprising the aqueous solution of melamine-formaldehyde resin modifiedwith sulfanilic acid, prepared by the process in the first aspect.

A third aspect of the present invention is a cement compositioncomprising the following component (I) and component (II):

Component (I): an aqueous solution of sulfonated melamine-formaldehyderesin obtained by a series of steps comprising of reacting (i) melamine,(ii) formaldehyde and (iii) a compound selected from the groupconsisting of a sulfate, a sulfite, a bisulfate, a bisulfite, apyrosulfate, a pyrosulfite, sulfamic acid and sulfanilic acid inalkaline medium, conducting a condensation reaction by adding an acid,and then adding an alkali; and

Component (II): a setting retarder.

A fourth aspect of the present invention is the cement composition asdescribed in the third aspect, wherein sulfanilic acid is used as thecompound (iii) in the production of component (I).

A fifth aspect of the present invention is the cement composition asdescribed in the third aspect, wherein the compound (I) is an aqueoussolution of melamine-formaldehyde resin modified with sulfanilic acidthat is produced in the process as described in the first aspect.

A sixth aspect of the present invention is the cement composition asdescribed any one of the third to fifth aspects, wherein the settingretarder of component (II) is aliphatic carboxylic acid, oxycarboxylicacid, oxycarboxylate, dicarboxylic acid, dicarboxylate, ketocarboxylicacid, ketocarboxylate, ligninsulfonate, sugar, hexafluorosilicate,cellulose ether, alkylaminophosphoric acid compound or their mixtures.

A seventh aspect of the present invention is the cement composition asdescribed any one of the third to fifth aspects, wherein the settingretarder of component (II) is oxycarboxylate, lignin sulfonate,hexafluorosilicate or their mixtures.

PRACTICAL EMBODIMENT OF THE INVENTION

The melamine, formaldehyde and sulfanilic acid used in the step (A) inthe first aspect of the present invention can be general industrialproducts, and can be commercially available. Examples of the industrialproducts of formaldehyde include formalin and paraformaldehyde. Examplesof the preferable alkali that is added for pH adjustment include sodiumhydroxide and potassium hydroxide.

In step (A), an amino group-containing compound other than malamine,such as urea, guanamine, dicyandiamide or thiourea, can be contained inthe proportion of up to 0.2 mole, calculated as amino group in the aminogroup-containing compound, per mole of amino group in melamine.

The aqueous solution containing the component (a), component (b),component (c) and component (d) can be formed such that melamine,formaldehyde and sulfanilic acid are added to water as a medium inproportions such that formaldehyde is 2.5-3.5 moles per mole of melamineand sulfanilic acid is 0.5-1.5 moles per mole of melamine, and an alkaliis added in an amount such that pH of the aqueous solution containingthe components (a) to (d) is 8.0-13.5. The amount of those materialsthat are added to water as a medium to form a reaction mixture ispreferably based on that melamine is about 5-70 parts by weight per 100parts by weight of water. In either of the steps (A) to (C),concentration by, for example, concentration under reduced pressure ordilution by addition of water can be conducted.

In the step (A), the aqueous solution containing the components (a) to(d) thus formed is heated at the temperature of 50-90° C. preferablywith stirring. During heating, pH of the aqueous solution is preferablymaintained at 8.0 or higher. The heating is conducted until sulfanilicacid is decreased to 40-90 mol % of the amount thereof charged. Theheating can generally be completed for about 10-180 minutes. In the step(A), methylol melamine is formed by the reaction of melamine andformaldehyde, and an initial condensate in which methylol melamine andsulfanilic acid are bonded in a certain form is formed. Thus, an aqueoussolution of sulfanilic acid modified methylol melamine is formed in thestep (A). The product after completion of the step (A) is a transparentliquid and generally has a pH of 8.0 or higher.

In the step (B), a solution having a pH of 6.0-8.0 is formed by addingan inorganic acid to the solution containing the initial condensateobtained in the step (A) after, preferably immediately after, completionof the step (A). Preferable examples of the inorganic acid added includemineral acids such as hydrochloric acid, sulfuric acid or nitric acid,and sulfamic acid. The solution thus prepared is heated to 50-90° C. Theheating is conducted until sulfanilic acid added to the reaction mixtureis decreased to 20-60 mol % of the amount thereof charged. The heatingcan generally be completed for about 10-360 minutes. The step (B) is astep to further bond unreacted sulfanilic acid that is present in thereaction liquid obtained in the step (A) with methylol melamine and alsoto form an aqueous solution of a melamine-formaldehyde resin modifiedwith sulfanilic acid by polycondensation reaction between methylolgroups in the initial condensate. At this time, the unreacted sulfanilicacid is decreased to 20-60 mol % of the amount of sulfanilic acidcharged in the step (A). For example, where sulfanilic acid is decreasedto 80 mol % of the amount thereof charged in the step (A), reaction isfurther conducted in the step (B) and heating is conducted untildecreasing to 20-60 mol %. Further, where sulfanilic acid is decreasedto 40 mol % in the step (A), reaction is further conducted untildecreasing to a range of 20 to less than 40 mol % in the step (B).

In the step (C), an aqueous solution having a pH of 7.0-14.0 is formedby adding an alkali to the solution formed in the step (B) after,preferably immediately after, completion of the step (B). The addedalkali that can be used is preferably the above-exemplified compoundsused in the step (A). Thus, a water reducing agent aqueous solution ofmelamine-formaldehyde resin modified with sulfanilic acid of the presentinvention can be produced. (—SO₃H) or (—SO₃M) is formed depending on apH of the resin aqueous solution obtained. M represents an alkali metalatom.

The aqueous solution of melamine-formaldehyde resin modified withsulfanilic acid obtained in the step (C) has a concentration of 15-60%by weight and a viscosity of 5-100,000 mPa·s.

If the proportion of formaldehyde to melamine is changed andformaldehyde is used in an amount of less than 2.5 moles per mole ofmelamine in the step (A), a large amount of free sulfanilic acid ispresent or it is difficult to form a melamine-formaldehyde resin, whenheated in the step (B) Further, a water reducing agent having highperformance is not obtained. Also, if formaldehyde is used in a largeamount exceeding 3.5 moles per mole of melamine, stability of the resinbecomes poor, which is not preferable. If the proportion of sulfanilicacid to melamine is changed and sulfanilic acid is used in an amount ofless than 0.5 mole per mole of melamine, the liquid formed in the step(C) does not have a sufficient stability. Also, if sulfanilic acid isused in an amount exceeding 1.5 moles per mole of melamine, freesulfanilic acid in the step (B) exceeds 60 mol % of the charged amount,and the free sulfanilic acid is present in excess in the liquid, whichis economically disadvantageous. If a pH of the reaction mixture ischanged and adjusted to a pH lower than 8.0 in the step (A), melamineresin formation proceeds and an abnormal reaction such as gelation mayoccur. Further, even if the pH is adjusted to a pH exceeding 13.5,unnecessary alkali is consumed, which is not economical. If the heatingtemperature is changed and the heating is conducted at a temperaturelower than 50° C. in the step (A), formation of the sulfanilic acidmodified methylol melamine becomes slow and this is not suitable to theproduction process for industrial production. If the heating isconducted at a temperature higher than 90° C., by-products such ascondensate of formaldehyde are formed, and a stable production cannot becarried out. If the heating is conducted until the detection degree ofsulfanilic acid is less than 40 mol % in the step (A), the liquidobtained in the step (C) has good water reducing performance, but haspoor fluidity retention effect. Further, if the step (B) is proceededwith the detection degree exceeding 90 mol %, resin formation is fastand an abnormal reaction such as gelation may occur.

If the pH is adjusted to less than 6.0 in the step (B), resin formationproceeds rapidly in the heating, which results in easy gelation. If thepH is adjusted to higher than 8.0, resin formation requires a long time.If the heating temperature is changed and heating is conducted at atemperature lower than 50° C. in the step (B), resin formation becomesslow, and if heating is conducted at a temperature higher than 90° C.,resin formation becomes fast, which may result in unusual reaction suchas gelation. If the heating time is 10 minutes or less in the step (B),the water reducing performance may become remarkably poor, and if itexceeds 360 minutes, gelation occurs in heating or a water reducingagent with high performance cannot be obtained. If the detection degreeof sulfanilic acid in the step (B) is less than 20 mole %, waterreducing performance is good, but fluidity retention effect is poor. Ifit exceeds 60 mol %, water reducing performance decreases.

If the pH is adjusted to less than 7.0 by adding an alkali in the step(C), resin formation proceeds during storage, and gelation occurs. Evenif the pH is adjusted to a pH exceeding 13.5, stability of the resindoes not change, and unnecessary alkali is consumed, which is noteconomical.

The second aspect of the present invention is the cement compositioncontaining the aqueous solution of melamine-formaldehyde resin modifiedwith sulfanilic acid obtained by the production process as described inthe first aspect.

In more detail, the cement composition is such that the aqueous solutionof melamine-formaldehyde resin modified with sulfanilic acid is added toa concrete, a mortar or a cement paste, and the resin aqueous solutioncan be added in the proportion of 0.1 to 5.0% by weight as a resin solidcontent based on the weight of the cement.

Further, as the third aspect of the present invention, the cementcomposition can be mentioned, which contains an aqueous solution ofmelamine-formaldehyde resin modified by sulfanilic acid as described inthe first aspect or by a modifying agents other than sulfanilic acid,and the setting retarder.

In more detail, it is the cement composition containing an aqueoussolution of the sulfonated melamine-formaldehyde resin for a waterreducing agent as the component (I) and the setting retarder as thecomponent (II).

The aqueous solution of sulfonated melamine-formaldehyde resin as thecomponent (I) is an aqueous solution of a resin comprising a sulfonatedmelamine formaldehyde condensate obtained by a step of reacting (i)melamine, (ii) formaldehyde and (iii) a sulfonic acid group introducingagent in molar ratios of (i):(ii):(iii)=1:2.5-3.5:0.5-1.5 in an alkalimedium at a pH of 8.0-13.5, a step of conducting condensation reactionby the addition of an acid, and a step of adding an alkali. This aqueoussolution has a pH of 7.0-13.5, a resin concentration of 15-60% by weightand a viscosity of 5-100,000 mPa·s.

The sulfonic acid group introducing agent (iii) is a compound selectedfrom the group consisting of a sulfate, a sulfite, a bisulfate (i.e.,hydrogensulfate), a bisulfite (i.e., hydrogensulfite), a pyrosulfate(i.e., disulfate), a pyrosulfite (i.e., disulfite), sulfamic acid (i.e.,amidosulfuric acid) and sulfanilic acid (i.e., p-aminobenzenesulfonicacid). Examples of the above salts include salts of alkali metals suchas lithium, sodium or potassium, salts of alkaline earth metals such asmagnesium, calcium, strontium or barium, and ammonium salts. Thesulfonic acid group introducing agent (iii) particularly preferably usedis sulfanilic acid.

Examples of the alkali used for pH adjustment include sodium hydroxideand potassium hydroxide.

It is preferable for the aqueous solution of sulfonatedmelamine-formaldehyde resin as the component (I) to use an aqueoussolution of melamine-formaldehyde resin modified with sulfanilic acidpreferably produced by the process as described in the first aspect ofthe present invention.

Examples of the component (II) include aliphatic carboxylic acid,oxycarboxylic acid, oxycarboxylate, dicarboxylic acid, dicarboxylate,ketocarboxylic acid, ketocarboxylate, lignin sulfonate, sugar,hexafluorosilicate, cellulose ether, alkylaminophosphoric acidcompounds, and their mixtures. Examples of the above salts include saltsof alkali metals such as lithium, sodium or potassium, salts of alkalineearth metals such as magnesium, calcium, strontium or barium, andammonium salts. Example of the aliphatic carboxylic acid includesheptanoic acid. Examples of the oxycarboxylic acid (hydroxycarboxylicacid) or its water-soluble salt include gluconic acid, glycolic acid,α-oxybutyric acid, citric acid, tartaric acid, malic acid, lactic acid,salicyclic acid (o-hydroxybenzoic acid), p-hydroxybenzoic acid, gallicacid and their water-soluble salts. Examples of the dicarboxylic acid orits water-soluble salt include maleic acid and its water-soluble salt.Examples of the ketocarboxylic acid or its water-soluble salt includespyruvic acid and its water-soluble salt. Examples of the sugar includesaccharose, glucose and malt sugar. Examples of the cellulose etherinclude methyl cellulose, ethyl cellulose, benzyl cellulose, tritylcellulose, cyan ethyl cellulose, carboxymethyl cellulose, carboxyethylcellulose, aminoethyl cellulose and hydroxyethyl cellulose.

Particularly preferable component (II) is oxycarboxylate, ligninsulfonate, hexafluorosilicate or their mixtures. For example, sodiumgluconate, sodium lignin sulfonate and magnesium hexafluorosilicate(i.e., magnesium silicofluoride). Those setting retarders can be used inthe form of a solid, a powder or an aqueous solution.

The cement composition of the present invention is such that thecomponent (I) and component (II) are added to a concrete, a mortar or acement paste. The aqueous solution of sulfonated melamine-formaldehyderesin as a water reducing agent of the component (I) can be added in theproportion of 0.1-5.0% by weight in terms of a resin solid content basedon the weight of the cement. Further, the setting retarder of thecomponent (II) can be added in the proportion of 0.005-3.000% by weightin terms of a solid content based on the weight of the cement. Of thesetting retarders, the gluconate can be added in the proportion of 0.01to 0.10% by weight in terms of a solid content based on the weight ofthe cement, lignin sulfonate can be added in the proportion of0.005-2.000% by weight in terms of a solid content based on the weightof the cement, and the hexafluorosilicate can be added in the proportionof 0.005-2.000% by weight in terms of a solid content based on theweight of the cement.

The present invention is described in more detail by reference to thefollowing examples, but the invention is not limited thereto.

EXAMPLE 1

The following aqueous solutions of water reducing agent T1 to T6 wereprepared. Preparation of water reducing agent T1:

Step (A): 326 g of water, 131 g of a 32 wt % aqueous solution of sodiumhydroxide, 173 g of sulfanilic acid, 268 g of a 37 wt % aqueous solutionof formaldehyde and 126 g of melamine were added with stirring to forman aqueous solution having a pH of 12.8. This aqueous solution washeated to 70° C. with stirring, and the heating was continued tomaintain this temperature until the amount of sulfanilic acid, which wasdecided by liquid chromatography analysis, became 60% of the chargedamount.

Step (B): Immediately after completion of the step (A) 88 g of water and4 g of 75 wt % sulfuric acid were added to the solution with stirring toform a solution having a pH of 7.0. This solution was maintained at 70°C. with stirring and the heating was continued for 150 minutes.

Step (C): Immediately after completion of the step (B), a 32 wt % sodiumhydroxide solution was added to the solution and cooled. By thisprocedure, an aqueous solution of melamine-formaldehyde resin modifiedwith sulfanilic acid, having a concentration of 38%, a pH of 12.5 and aviscosity of 30 mPa·s was obtained. The amount of free sulfanilic acidwas 50% of the charged amount. Preparation of water reducing agents T2to T6:

An aqueous solutions of sulfanilic acid modified melamine-formaldehyderesin T2 to T6 were obtained in the step (C) by changing the conditionsof Example 1 in the preparation of the aqueous solution of waterreducing agent T1 to the conditions shown in Table 1. S detection degree(mol %) (=S det. degr.(mol %))in the step (A) and the step (B) in theTable shows the amount (mol %) of unreacted free sulfanilic acidremained in the aqueous solution based on the charged amount. Theviscosity is expressed by mPa·s. The abbreviations in the Tables havethe following meanings: aqu. sol. of wat. red. agent=aqueous solution ofwater reducing agent, conc.=concentration, visc.=viscosity.

TABLE 1 step (A) step (B) aqu. sol. of S det. S det. step (A) wat. red.T degr. T time degr. conc. agent pH (° C.) (mol %) pH (° C.) (m) (mol %)pH (wt %) visc. T1 12.8 70 60 7.0 70 150 50 12.5 38 30 T2 12.8 70 80 7.570 250 50 12.5 38 40 T3 12.0 70 50 7.0 70 150 40 12.5 38 35 T4 11.0 6070 6.5 60 120 60 12.5 38 50 T5  9.0 60 50 7.5 60 200 30 12.5 38 100  T611.0 80 80 7.0 80  60 60 12.5 38 50

EXAMPLE 2

Aqueous solutions of sulfanilic acid modified melamine-formaldehyderesin T7 to T10 were obtained in the step (C) by changing the conditionsof Example 1 in the preparation of the water reducing agent aqueoussolution T1 to the elements shown in Table 2, in which F/M means a molarratio of formaldehyde/melamine, and S/M means a molar ratio ofsulfanilic acid/melamine.

TABLE 2 step (A) step (B) aqu. sol. of S det. S det. step (C) wat. red.degr. time degr. conc. agent F/M S/M (mol %) pH (m) (mol %) pH (wt %)visc. T7  2.5 1.0 60 7.0 280 50 12.5 38 80 T8  3.5 1.0 60 6.5 120 4012.5 38 60 T9  3.0 1.5 70 7.0 200 60 12.5 41 40 T10 3.0 0.5 60 7.0 15040 12.5 33 60

EXAMPLE 3

A concrete was prepared with unit amounts of water/cement ratio(W/C):47%, fine aggregate degree (s/a):44%, cement: 350 kg/m³, water:165 kg/m³, fine aggregate (S): 777 kg/m³ and coarse aggregate (G): 997kg/m³. The cement was normal Portland cement, the fine aggregate wassand produced in Toyama, and the coarse aggregate was crushed stone 2005produced in Hachioji. Each of the water reducing agent aqueous solutionsT1 to T10 obtained by the production process of the present inventionand sodium gluconate were blended in the proportion to the cement asshown in Table 3, and the change with time in slump value was measured.(C×%) in Table 3 shows the amount (wt % solid content) of the waterreducing agent aqueous solution and the setting retarder added to thecement.

Further, as a commercially available water reducing agent, an aqueoussolution of sulfonated melamine-formaldehyde resin modified with sodiumsulfite (T11) having a pH of 12, a concentration of 35 wt % and aviscosity of 30 mPa·s and an aqueous solutin of sulfonatedmelamine-formaldehyde resin modified with sodium sulfite (T12) having apH of 8, a concentration of 23 wt % and a viscosity of 8 mPa·s wereused.

Further, a setting retarder (S1) comprising sodium gluconate as a maincomponent, a setting retarder (S2) comprising sodium lignin sulfonate asa main component or a setting retarder (S3) comprising magnesiumhexafluorosilicate as a main component was used as an aggregation andsetting retarding component of the cement composition.

Concrete (40 liters) was produced using a 50 liters pan type forcedkneading mixer. The kneading method was that a mortar having a waterreducing agent aqueous solution added thereto was kneaded for 30seconds, coarse aggregates were introduced therein, and the resultingmixture was kneaded for 90 seconds and then discharged from the mixer.The slump was measured immediately after discharging the concrete fromthe mixer, after 30 minutes from the discharging and after 60 minutesfrom the discharging. The concrete after discharging was agitated in a50 liters gravity type mixer at 2 rpm and then stored. Amount of air ina fresh concrete was adjusted to 4.5% with AE agent (air entrainingagent).

The results of tests conducted based on the above test methods are shownin Table 3.

TABLE 3 water reducing setting agent retarder change in slump value (cm)added added 30 60 amount amount immediately minutes minutes No. C × %No. C × % after the discharge T1  0.4 — 0 18.5 15.5 13.0 T2  0.4 — 017.0 16.0 12.5 T3  0.4 — 0 18.0 15.0 12.5 T4  0.4 — 0 18.0 15.5 13.0 T5 0.4 — 0 19.0 16.5 13.5 T6  0.4 — 0 18.5 16.0 12.5 T7  0.5 — 0 17.0 15.012.0 T8  0.4 — 0 18.0 16.5 12.5 T9  0.4 — 0 17.5 15.0 12.0 T10 0.5 — 018.5 16.0 13.5 T11 0.6 — 0 17.0 11.0  5.0 T12 0.6 — 0 17.5  8.5  3.5 T1 0.4 S1 0.02 18.5 18.0 17.5 T1  0.4 S2 0.02 19.0 16.5 16.0 T1  0.4 S30.02 18.5 17.5 15.0 T2  0.4 S1 0.02 18.5 17.5 16.0 T2  0.4 S2 0.02 17.516.0 14.5 T2  0.4 S3 0.02 18.5 17.5 15.0 T11 0.6 S1 0.02 18.0 13.5  8.0T12 0.6 S1 0.02 18.0 11.0  7.0 T1  0.4 S1 0.05 18.0 18.0 17.0 T1  0.4 S20.05 17.5 16.0 15.0 T1  0.4 S3 0.05 18.0 16.5 15.5 T2  0.4 S1 0.05 18.517.0 15.5 T2  0.4 S2 0.05 17.5 17.0 15.0 T2  0.4 S3 0.05 18.0 16.5 15.0T11 0.6 S1 0.05 18.5 14.0  9.5 T12 0.6 S1 0.05 17.0 13.5  8.5 T1  0.4 S10.10 19.0 19.5 19.5 T1  0.4 S2 0.10 18.0 18.0 16.5 T1  0.4 S3 0.10 18.017.0 17.0 T2  0.4 S1 0.10 18.5 18.0 19.0 T2  0.4 S2 0.10 17.5 18.0 16.0T2  0.4 S3 0.10 18.0 17.5 16.5 T3  0.4 S1 0.10 18.5 18.0 18.0 T4  0.4 S10.10 19.0 18.5 18.0 T5  0.4 S1 0.10 18.0 19.0 17.5 T6  0.4 S1 0.10 17.017.5 18.5 T7  0.5 S1 0.10 17.5 17.0 18.0 T8  0.4 S1 0.10 18.5 18.5 17.0T9  0.4 S1 0.10 19.0 19.0 19.0 T10 0.5 S1 0.10 18.5 18.0 17.5 T11 0.6 S10.10 18.0 15.0  9.5 T12 0.6 S1 0.10 19.0 14.5  9.0 T1  0.4 S1 0.20 17.518.5 19.0 T1  0.4 S2 0.20 17.5 18.0 17.0 T1  0.4 S3 0.20 18.0 17.0 16.5T2  0.4 S1 0.20 18.0 19.0 18.5 T2  0.4 S2 0.20 17.0 16.0 16.0 T2  0.4 S30.20 17.5 16.0 15.5 T11 0.6 S1 0.20 18.0 15.0 10.0 T12 0.6 S1 0.20 18.516.0  9.5

When the setting retarder is added in an amount of 0.005% or more byweight as a solid content based on the weight of the cement, the effectthereof is exhibited, and the effect is markedly exhibited by adding0.02% by weight or more of the setting retarder. The effect reaches itssaturation when the setting retarder is added in an amount of 3.00% byweight as a solid content, and addition exceeding 3.00% by weight doesnot provide an economical effect that is commensurate with the additionamount.

When the same amount of setting retarders is added, the gluconaterepresented by sodium gluconate exhibits the most excellent retardationeffect (fluidity retention effect), and the ligninsulfonate representedby sodium lignin sulfonate and the hexafluorosilicate represented bysodium hexafluorosilicate are next best.

The most preferable combination is the aqueous solution ofmelamine-formaldehyde resin modified with sulfanilic acid as a waterreducing agent of the component (I) and the setting retarder of thecomponent (II), but a combination of the A aqueous solution ofsulfonated melamine-formaldehyde resin prepared with sodium sulfite thatis conventionally used as the component (I) and the above settingretarder of the component (II) can also be applied.

According to the present invention, when the aqueous solution ofmelamine-formaldehyde resin modified with sulfanilic acid obtained inthe step (C) by controlling the reaction rate of sulfanilic acid in thestep (A) and the step (B) is added to a cement composition as a waterreducing agent, the cement composition has excellent water reducingperformance and high fluidity retention effect. Therefore, even if amortar or a concrete is produced and then allowed to stand for hours forvarious reasons, the cement composition can easily be poured into a moldframe or the like.

Further, if the aqueous solution of melamine-formaldehyde resin modifiedwith sulfanilic acid is used in combination with a setting retarder,i.e., a substance that retards hydration and setting reaction of acement composition, it becomes possible to further increase the fluidityretention effect of the melamine-formaldehyde resin and sulfanilic acidmodified melamine-formaldehyde resin.

Further, addition of the setting retarder to a concrete or a mortarexhibits the fluidity retention effect by a method of adding the settingretarder in the form of a solid, a method of adding the setting retarderin the form of an aqueous solution or a method of dissolving the settingretarder in a chemical miscible agent including an aqueous solution of awater reducing agent and then adding the resulting mixture. The timewhen the setting retarder is added is considered the case ofsimultaneously adding the same together with the water reducing agentand water, the case of adding the same to a cement or an aggregate orthe case of adding the same after preparing a concrete or a mortar.However, use of either method can exhibit the fluidity retention effect.

The concrete or mortar having thus increased fluidity retention effectcan be applied to concrete product factories in which themelamine-formaldehyde resin has conventionally been used, and also to aready mixed concrete or the like in which the melamine-formaldehyderesin has not conventionally been used so much. Further, such a concreteor mortar is very effective in a summer season in which decrease influidity with time particularly becomes a problem, or in preventingdecrease in fluidity with time in the case that a kneading temperatureof a concrete is relatively high.

What is claimed is:
 1. A cement composition comprising: a cementcomponent selected from the group consisting of concrete, mortar, and acement paste, and an aqueous solution of melamine-formaldehyde resinmodified with sulfanilic acid; wherein the aqueous solution is preparedby a first step comprising adjusting an aqueous solution of melamine(a), formaldehyde (b), sulfanilic acid (c), and an alkali substance (d)to (a):(b):(c)=1:2.5-3.5:0.5-1.5 in molar ratio and its pH to 8.0-13.5,and thereafter heating the aqueous solution at 50-90° C. to conduct thereaction until free sulfanilic acid decreases to 40-90 mol % of theamount of sulfanilic acid charged; wherein the aqueous solution isfurther prepared by a second step comprising adding an inorganic acid tothe reaction liquid obtained in the first step to adjust its pH to6.0-8.0, and thereafter heating the reaction liquid at 50-90° C. toconduct the reaction until free sulfanilic acid decreases to 20-60 mol %of the amount of sulfanilic acid charged; and wherein the aqueoussolution is further prepared by a third step comprising adjusting a pHof the reaction liquid obtained in the second step to 7.0-13.5.
 2. Thecement composition according to claim 1, further comprising a settingretarder.
 3. A cement composition comprising: a cement componentselected from the group consisting of concrete, mortar, and a cementpaste, and the following components (I) and (II): component (I): anaqueous solution of sulfonated melamine-formaldehyde resin obtained by aseries of steps comprising reacting (i) melamine, (ii) formaldehyde and(iii) sulfanilic acid in an alkaline medium, conducting a condensationreaction by adding an acid, and then adding an alkali; and component(II): a setting retarder.
 4. The cement composition according to claim3, wherein the setting retarder of component (II) is selected from thegroup consisting of aliphatic carboxylic acid, oxycarboxylic acid,oxycarboxylate, dicarboxylic acid, dicarboxylate, ketocarboxylic acid,ketocarboxylate, lignin sulfonate, sugar, hexafluorosilicate, celluloseether, alkylaminophosphoric acid compound and mixtures thereof.
 5. Thecement composition of claim 3, wherein the setting retarder of component(II) is selected from the group consisting of oxycarboxylate, ligninsulfonate, hexafluorosilicate and mixtures thereof.
 6. The cementcomposition according to claim 3, wherein the setting retarder ofcomponent (II) is selected from the group consisting of aliphaticcarboxylic acid, oxycarboxylic acid, oxycarboxylate, dicarboxylic acid,dicarboxylate, ketocarboxylic acid, ketocarboxylate, lignin sulfonate,sugar, hexafluorosilicate, cellulose ether, alkylaminophosphoric acidcompound and mixtures thereof.
 7. The cement composition according toclaim 3, wherein the setting retarder of component (II) is selected fromthe group consisting of oxycarboxylate, lignin sulfonate,hexafluorosilicate and mixtures thereof.
 8. The cement composition ofclaim 7, wherein the setting retarder is selected from the groupconsisting of aliphatic carboxylic acid, oxycarboxylic acid,oxycarboxylate, dicarboxylic acid, dicarboxylate, ketocarboxylic acid,ketocarboxylate, lignin sulfonate, sugar, hexafluorosilicate, celluloseether, alkylaminophosphoric acid compound and mixtures thereof.
 9. Thecement composition of claim 7, wherein the setting retarder is selectedfrom the group consisting of oxycarboxylate, lignin sulfonate,hexafluorosilicate and mixtures thereof.